Danny Alexander has called on the Scottish Government to produce its own "realistic analysis" of the cost of independence as the Treasury prepares to publish its findings on the financial impact of a Yes vote "in more detail than ever before".

The Chief Secretary to the Treasury will use a speech in Edinburgh on Wednesday to launch a fresh attack on the proposals set out in the SNP administration's white paper on independence, focusing on what he described as "over-optimistic assumptions" about oil revenues.

His latest intervention comes a few weeks before the Treasury's most detailed fiscal analysis is due to be published.

Chancellor George Osborne and Mr Alexander asked the department's economists to calculate "in detail the figures that illustrate the benefits of the UK and the cost of independence".

Economists have spent months analysing data and forecasts, and consulting with independent bodies, the UK Government said.

The analysis will set out "in more detail than ever before the impact of having to absorb the higher spending and lower tax caused by declining oil revenues, an ageing population, the Scottish Government's uncosted policy pledges and the set-up costs of independence in a much smaller budget".

Treasury officials have also analysed the Scottish Government's white paper and have "attempted to produce many of the calculations that were missing".

Mr Alexander said: "The Scottish Government's white paper contained lots of promises but nothing credible to back it up.

"People are beginning to realise that they can't answer even the most basic questions.

"It's damning that the only credible paper we've seen from the Scottish Government is their finance minister's secret leaked paper warning about the cuts and tax rises needed to pay for declining oil revenues and an ageing population. If their promises seem too good to be true, it's because they are."

He added: "This week I will also be challenging some of the myths of independence - people need to know the facts.

"The problems of declining oil revenues and an ageing population cannot simply be wished away - but the broad shoulders of the UK can help absorb them."

The Scottish Government's estimates on oil revenues contrast with forecasts made by the Office for Budget Responsibility (OBR), the UK Government's fiscal watchdog.

The OBR estimates oil revenues will be around £3.2 billion in 2016, which would be the first year of independence, compared with Scottish Government figures which put them as high as £7.9 billion.

A spokesman for the Scottish Government said: "The fact is Scotland is one of the wealthiest countries per head in the world and is more than capable of being an economically successful independent country - the fiction is coming from Mr Alexander and his colleagues in the Tory-led No campaign.

"Scotland has the financial resources to be a successful independent nation.

"In each of the last 32 years, tax receipts per person in Scotland have been higher than the UK as a whole, and in 2011-12 it was in a stronger fiscal position than the UK to the tune of £4.4 billion, or £824 per person.

"Scotland would have had the opportunity to spend more, tax less, invest in an oil fund, and still borrow proportionally less than the UK.

"Independence will provide Scotland with the opportunity to take spending decisions which better reflect the needs and desires of the Scottish people and the Scottish economy.

"For example, not replacing Trident would free up substantial resources that could put to use delivering better pensions for Scotland's elderly."